@fjn04 1,385 posts03-20-2020 9:35pm... The mono 120’s are more of a KT 150 amp by design, although I believe 88’s are ok.--------------------------------------------------------
Yes, the QS Mono 120 amplifiers really are designed for KT150s with the larger transformers and higher plate voltages. In my Mono 120s I started wth KT120s, was going to try KT88s next, but Mike @Quicksilver discouraged me from doing so. Popped in a matched quad of KT150s and wallah, never looked back. I’m a diehard EL34 convert now. Like the KT150s more than I thought I would (especially when paired with really good input tubes to sweeten them up). There is a tad more air on top, more weight on bottom, added dynamics - nice linear midrange from KT150s. The real music comes in with good input tubes and 100-200hrs on caps and KT150s. Amazing with electrostatic speakers too. A few other tips to share privately offline.
My Mono 120s were stocked with decent EI 12AU7 inputs and basic JJ 12AT7 driver tubes which sounded decent. Tried a few others. Finally, had to..., 1960s Mullard Blackburns and wow, really nice.
Mid Monos, Mono 60s, Mono 120s. Can’t lose. Point to point, quality build, great value, all very nice. Put a really nice preamp in front of them and they really do compete with amps at 2-3x the price.
---------------------
Oh, and, a buddy just bought the Mid Monos. Dropped in some vintage input tubes. The Mid Monos just displaced his higher $ rig now up for sale.